In recent years there has been a steady growth in the use of polymeric compositions as a substitute for wood and other materials of construction in building applications. In particular, there has been an increased use of rigid polyvinyl chloride in place of wood for house sidings. This polymeric material has many decorative and structural characteristics that are desired, and it can be blended with a wide variety of inorganic pigments to give an infinite number of colors and hues.
One of the problems with polyvinyl chloride compositions is their tendency to oxidize and degrade. Oxidized polyvinyl chloride becomes brittle and cracks in a very short time. Accordingly, one desirable characteristic of the pigments and other additives that are blended with the vinyl chloride is their ability to reflect infra red rays. A highly infra red reflective siding will remain cooler when exposed to sunlight than a siding containing additives which readily absorb many of these infra red rays. Lower temperatures mean a lower heat build-up within the structure and longer life for the siding. A reduction of a few degrees in the heat build-up translates into a substantial increase in the life of the siding.
The standard procedure for preparing metal oxide pigments consists of calcining an intimate mixture of oxides or oxide precursors of primarily transition metals. Color properties develop from the formation of solid solutions containing the transition metals having colored ions. Colors produced by calcining essentially white pigments with small additions of foreign elements to produce stable tinted pigments have been commercially developed over the last 30 years. For example, titanium dioxide becomes colored when calcined with minor amounts of transition metals.
Metal oxide pigments are widely used as colorants in the paint, plastics and ceramics industries and they are principally known for their chemical, thermal and weathering stabilities. While the same basic pigment compositions can be used by these industries to color the various medias ranging from complex organic polymers to glass, it is often necessary to adjust the physical properties of each pigment to meet the specifications for its successful commercial application. For example, a ceramic color is composed usually of coarser particles to minimize dissolution in the strong alkaline glazes and thereby maintain color intensity. Conversely, the paint and plastics industries prefer pigments in a relatively finely divided state to permit easy dispersion and optimize properties of gloss, brightness, strength and opacity. For tinted paints, the necessity of introducing a separate colored pigment can in certain cases introduce weak features as far as their stability to light, heat, solvents and chemicals are concerned resulting in flotation, flocculation, recrystallization, sublimation and chalking. The use of "tinted white" or "titanate pigments" offers a way to overcome the difficulties associated with unstable tinted systems without departing from the whitening, hiding and other valuable pigmentary properties inherent in the "host" element which in this instance is titanium dioxide.
A large number of pigments in which the major component is a white pigment such as titanium dioxide which accepts minor additions of intensely colored metal ions to produce pastel colorants are described in U.S. Pat. No 3,022,186. This patent describes solid solutions resulting from a large number of combinations of metal oxides or fluorides as guest components in a number of host lattices, but principally rutile titanium dioxide. The pigments prepared or disclosed in U.S. Pat. No. 3,002,186, while possessing the desired color values, are generally deficient in some physical characteristics such as texture, i.e., ease of dispersibility, gloss and opacity necessary for commercial use in the paint and plastics industries. Of the various combinations of metals described in the '186 patent, manganese (III) and tungsten (VI) are described as metals which can be incorporated into the solid solutions. Example 5 describes a pigment prepared from anatase, manganese oxide and tungsten oxide. The resulting pigment is reported to be a dark red-brown pigment. In Example 13, the same components are mixed in different amounts and a pale pink to reddish brown pigment is reported to be formed.
Reissue Pat. No. Re 21,427 describes the process for forming titanium dioxide pigments by combining the titanium dioxide with a compound of a heavy metal. Examples of heavy metals listed in Col. 1, lines 21-25 include vanadium, chromium, iron, cobalt, nickel, manganese and copper.
U.S. Pat. No. 3,956,007 describes antimony-free yellow pigments prepared by calcining anatase with a specified amount of nickel, tungsten, zinc, lithium, cerium and magnesium compounds.